In the E 350 BlueTEC, which comes fitted with the new 9G-TRONIC as standard, the 185 kW (252 hp) V6 diesel engine has an average NEDC fuel consumption of 5.3 liters of diesel per 100 kilometers, corresponding to CO2 emissions of 138 g/km. As a result, the new models with 9G-TRONIC undercut their predecessors in terms of both consumption and CO2 emissions. The higher number of gears and the broader gear ratio spread help to increase drive comfort and enable a significant enhancement to be achieved in terms of converting engine power into traction.

E 350 BlueTEC with V6 diesel engine and 9G-TRONIC

On the one hand, the overall reduction in engine speed improves NVH comfort and therefore the pleasant sense of well-being on board, and on the other also cuts down external noise by up to 4 dB(A), thus reducing the strain on the environment.

The reduced fuel consumption of the E 350 BlueTEC with 9G-TRONIC has primarily been achieved as a result of the efficiency of the transmission. As part of this, the ratio spread of 9.15 for gears one to nine enables a clearly perceptible reduction in engine speed and is a decisive factor behind the energy efficiency and ride comfort.

The ease of shifting of the new 9G-TRONIC – a focal point during development and a hallmark feature of a Mercedes-Benz automatic transmission – comes courtesy of a comprehensive package of measures. These include the direct control system which enables short, barely perceptible gear changes. The combination of double torsional damper and centrifugal pendulum technology in the torque converter ensures drive comfort. Together with the extended gear ratio spread, higher vehicle speeds can now be driven at lower engine speeds for even greater comfort. In reality this translates for example into being able to drive at 120 km/h in 9th gear with an engine speed of around only 1350 rpm.

Advanced technology for power transmission

In the case of the 9-speed automatic transmission, the development engineers also focused on the area of “compact lightweight construction”. Despite two additional gears and a maximum transferable torque of up to 1000 Newton meters, the new automatic transmission requires as little installation space as its predecessor and, in addition, is lighter. The two-piece housing design has been retained: the torque converter housing is made of lightweight aluminum, while the transmission housing with weight-optimized plastic oil pan is made of an even lighter magnesium alloy.

Another goal was to implement the nine gears with a minimal number of planetary gear sets and shift elements. Intensive, computer-based system analysis and mock-up made it possible to realize this goal with just four simple planetary gear sets and six shift elements. Three speed sensors monitor operation and provide the transmission control system with corresponding data for effective shifting. Here it is possible for several gears to be jumped when accelerating or decelerating, should the driving conditions call for it.

To ensure the reliable and at the same time highly efficient supply of the durable and shear-resistant 2nd-generation synthetic fuel economy engine oil, the new automatic transmission is fitted with two pumps. The smaller mechanical main pump, featuring an off-axis design, is located next to the main shaft and is chain-driven and fed by a separate electric auxiliary pump. This design enables the flow of lubrication and coolant to be controlled actively on demand and also means that the 9G-TRONIC can benefit from a start/stop system. Thanks to the world’s first direct control system in a planetary automatic transmission with nine gears, it has also been possible to significantly increase hydraulic efficiency within the transmission.

Romain’s opinion:

After ZF with its 9HP, Mercedes is also introducing a 9 speed automatic transmission in order to reduce fuel consumption of high end vehicles. Do you think that this will inverse the trend of decreased market shares for automatic transmission? Don’t you think that automatic transmission technology is slowly extinguishing?